Kenyan authorities have charged an IT expert with hacking into the country's tax authority and stealing almost $40m, according to local media.

Alex Mutunga Mutuku, 28, is accused of belonging to a syndicate of electronic fraudsters who steal money from various institutions and companies in the East African nation, The Standard newspaper reported.

"The information we have is just a tip of the iceberg. The racket is big and involves people outside the country," Edwin Okello, the state prosecutor, was quoted as saying on Wednesday.

Mutuku, who pleaded not guilty, allegedly hacked into the Kenya Revenue Authority's computer systems over the past two years.

The suspect, who routinely posted his lavish lifestyle on social media, was known to authorities and was arrested in 2015 on suspicion of hacking into the country's biggest telephone network provider, Safaricom, and stealing airtime worth $150, according to The Daily Nation newspaper.

Mutuku was accused in 2014 of hacking into the system of a local bank, the paper said.